Add pytest as core dependency (#290)

setup.py

@@ -20,7 +20,7 @@
 
 setup(
     name='funsor',
-    version='0.1.1',
+    version='0.1.2',
     description='A tensor-like library for functions and distributions',
     packages=find_packages(include=['funsor', 'funsor.*']),
     url='https://github.com/pyro-ppl/funsor',
@@ -29,27 +29,27 @@
     },
     author='Uber AI Labs',
     author_email='[email protected]',
+    python_requires=">=3.6",
     install_requires=[
         'multipledispatch',
         'numpy>=1.7',
         'opt_einsum>=2.3.2',
         'pyro-ppl>=0.5',
+        'pytest>=4.1',
         'torch>=1.3.0',
     ],
     extras_require={
         'test': [
             'flake8',
             'pandas',
-            'pytest>=4.1',
+            'pyro-api>=0.1',
             'pytest-xdist==1.27.0',
             'torchvision==0.2.1',
-            'pyro-api>=0.1',
         ],
         'dev': [
             'flake8',
             'isort',
             'pandas',
-            'pytest>=4.1',
             'pytest-xdist==1.27.0',
             'sphinx>=2.0',
             'sphinx_rtd_theme',